![]() Λ = The thermal conductivity of the material separating the medias (btu/ft2 h ☏) Δ = The thickness of the heat transfer surface (ft) Α2 = The heat transfer coefficient between the heat transfer surface and the cold medium (btu/ft2 h ☏) ![]() Α1 = The heat transfer coefficient between the warm medium and the heat transfer surface (btu/ft2 h ☏) The total overall heat transfer coefficient k is defined as: Heat transfer coefficient and design margin T4 = Outlet temperature - cold side LMTD can be calculated by using the following formula, where ∆T1 = T1–T4 and ∆T2 = T2–T3Ģ. K = heat transfer coefficient (btu/ft2 h ☏) Δt = temperature difference between inlet and outlet on one side (☏) The heat load of a heat exchanger can be derived from the following two formulas: 1. How do you calculate the heat transfer area of a plate heat exchanger? If the flow rate, specific heat and temperature difference on one side are known, the heat load can be calculated. The flowrate on the primary and secondary sides.The maximum allowable pressure drop on the primary and secondary sides.The inlet and outlet temperatures on the primary and secondary sides.The amount of heat to be transferred (heat load).The six most important parameters include: Accessed: 10 March, 2024.To solve a thermal problem, we need to know several parameters. Thermobacteriology in food processing, 2nd ed. (2020b). Calculation of equivalent time temperatures between 80° and 90☌ for the pasteurisation of ice cream mixes to meet the US Grade A Pasteurized Milk Ordinance (2017). How do you calculate the z-value given two equivalent thermal processes?. Go to the Thermal process equivalence calculator Literature cited This can be done using Equation 1 (Mullan 2020b). Calculation of equivalent time temperatures between 80° and 90☌ for the pasteurisation of ice cream mixes to meet the US Grade A Pasteurized Milk Ordinance (2017) This finding is significant and illustrates that the current HTST process for commercial milk is only equivalent in lethality terms to the older holder method of 63☌ for 30 minutes if the target pathogen has the same z-value as C. Using a lower estimate for z, say 8☌, the equivalent holding time at 72☌ can be calculated as 135 seconds. There is no agreement on the z-value of MAP but it is likely to be in the range 7☌-10 ☌.Īssuming a high value of 10 ☌, the equivalent holding time at 72☌ can be calculated using Equation 1 as 227 seconds. MAP is increasingly being linked to Crohn's Disease. paratuberculosis (MAP) as the target pathogen. This examples illustrates the basis of the current high temperature short time (HTST) treatment of milk.Ģ. Calculate the holding time at 72☌ that is equivalent to pasteurising milk at 63☌ for 30 minutes using Mycobacterium avium subsp. ![]() Knowing the z-value, the holding time at 72☌ can be calculated using Equation 1 as 15 seconds. burnetii has a z-value of 4.34☌ over the temperature range 60☌ to 72☌. The current target pathogen for milk pasteurisation is Coxiella burnetii. Calculate the holding time at 72☌ that is equivalent to pasteurising milk at 63☌ for 30 minutes. Further examples using milk pasteurisationġ. This has been discussed by Mullan (2020a). How do you find z if this value has not been provided?Įquation 1 can be solved for z. Note this approach should be used carefully since the linearity of the D-values (implied in the calculation) may only apply over a limited range of temperature. The same equation and approach to the calculation can also be used to calculate equivalent process lethality at a lower temperature. Going back to equation 1 we can now insert the -1.954 we have calculated.įinally, we can add the value for F ref and complete the calculation. Firstly breaking down the terms in the equation, we will first calculate: We will use equation 1 to do the calculation. The processor has installed a continuous pasteurizer and wishes to use a temperature of 102☌ to produce the drink. Calculate the holding time at 102☌, that will give an equivalent lethality to 85☌ for 15 minutes given the z-value is 8.7☌. The product was previously produced using a T ref of 85☌ and a holding time of 15 minutes. Providing that the F value at T ref and the z value are known then the F value at the required temperature, T, can be calculated using equation 1.Įquation 1 has been derived from Stumbo (1973).Īn example of how to use equation 1 is given for a fruit drink product. This article explains how to calculate an equivalent thermal or heat process at a higher or lower temperature and provides access to a free On Line calculator for checking your calculations. How does the processor calculate the equivalent process? ![]() There will be occasions when a food manufacturer wishes to use a different, but equivalent lethal thermal process.
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